Solar input spectra. Top: photo-absorption cross section of CO₂ at 250 K as the gray line. Overplotted as the dashed red line is the photodissociation cross section. For shorter wavelengths of the spectrum, the photoionizing energies have a threshold ≈80 nm. Bottom: Typical solar EUV/UV spectrum at 1 nm resolution, as observed by the MAVEN/EUM spectrograph, scaled at 1 AU, at different dates of the solar cycle.